Errors while updating project settings

Hi all,

I have a self hosted Gitlab instance and I’m facing a problem:
In one of my projects I cannot update project details, i.e. change the description, or reactivate the wiki.

From the logs I get this:

==> /var/log/gitlab/gitlab-rails/production.log <==
Started PATCH "/cometchaser/projectX" for X.X.X.X at 2020-07-28 19:44:32 +0000
Processing by ProjectsController#update as JS
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"[FILTERED]", "update_section"=>"js-general-   settings", "project"=>{"name"=>"projectX", "id"=>"15", "tag_list"=>"", "description"=>"[FILTERED]"}, "commit"=>"Save changes", "namespace_id"=>"cometchaser", "id"=>"projectX"}
Completed 500 Internal Server Error in 134ms (ActiveRecord: 22.3ms | Elasticsearch: 0.0ms | Allocations: 17733)

==> /var/log/gitlab/gitlab-rails/production_json.log <==
{"method":"PATCH","path":"/cometchaser/projectX","format":"js","controller":"ProjectsController","action":"update","status":500,"time":"2020-07-28T19:44:32.460Z","params":[{"key":"utf8","value":"✓"},{"key":"_method","value":"patch"},   {"key":"authenticity_token","value":"[FILTERED]"},{"key":"update_section","value":"js-general-settings"},{"key":"project","value":{"name":"projectX","id":"15","tag_list":"","description":"[FILTERED]"}},{"key":"commit","value":"Save changes"},{"key":"namespace_id","value":"cometchaser"},{"key":"id","value":"projectX"}],"remote_ip":"X.X.X.X","user_id":2,"username":"cometchaser","ua":"XXX","correlation_id":"dMJF5AaNlk6","meta.user":"cometchaser","meta.project":"cometchaser/projectX","meta.root_namespace":"cometchaser","meta.caller_id":"ProjectsController#update","redis_calls":1,"redis_duration_s":0.000428,"redis_read_bytes":181,"redis_write_bytes":585,"redis_shared_state_calls":1,"redis_shared_state_duration_s":0.000428,"redis_shared_state_read_bytes":181,"redis_shared_state_write_bytes":585,"queue_duration_s":0.008012,"cpu_s":0.13,"exception.class":"OpenSSL::Cipher::CipherError","exception.message":"","exception.backtrace":["lib/gitlab/crypto_helper.rb:27:in `aes256_gcm_decrypt'","app/models/concerns/token_authenticatable_strategies/encrypted.rb:45:in `get_token'","app/models/concerns/token_authenticatable_strategies/base.rb:27:in `ensure_token'","app/models/concerns/token_authenticatable_strategies/encrypted.rb:32:in `ensure_token'","app/models/concerns/token_authenticatable.rb:43:in `block in add_authentication_token_field'","app/services/projects/update_service.rb:31:in `execute'","app/controllers/projects_controller.rb:80:in `update'","app/controllers/application_controller.rb:491:in `set_current_admin'","lib/gitlab/session.rb:11:in `with_session'","app/controllers/application_controller.rb:482:in `set_session_storage'","app/controllers/application_controller.rb:476:in `set_locale'","lib/gitlab/error_tracking.rb:50:in `with_context'","app/controllers/application_controller.rb:541:in `sentry_context'","app/controllers/application_controller.rb:469:in `block in set_current_context'","lib/gitlab/application_context.rb:52:in `block in use'","lib/gitlab/application_context.rb:52:in `use'","lib/gitlab/application_context.rb:20:in `with_context'","app/controllers/application_controller.rb:462:in `set_current_context'"],"db_duration_s":0.0223,"view_duration_s":0.0,"duration_s":0.13863,"db_count":21,"db_write_count":1,"db_cached_count":1}

==> /var/log/gitlab/gitlab-rails/production.log <==

OpenSSL::Cipher::CipherError ():
  
lib/gitlab/crypto_helper.rb:27:in `aes256_gcm_decrypt'
app/models/concerns/token_authenticatable_strategies/encrypted.rb:45:in `get_token'
app/models/concerns/token_authenticatable_strategies/base.rb:27:in `ensure_token'
app/models/concerns/token_authenticatable_strategies/encrypted.rb:32:in `ensure_token'
app/models/concerns/token_authenticatable.rb:43:in `block in add_authentication_token_field'
app/services/projects/update_service.rb:31:in `execute'
lib/gitlab/metrics/instrumentation.rb:161:in `block in execute'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:161:in `execute'
app/controllers/projects_controller.rb:80:in `update'
app/controllers/application_controller.rb:491:in `set_current_admin'
lib/gitlab/session.rb:11:in `with_session'
app/controllers/application_controller.rb:482:in `set_session_storage'
lib/gitlab/i18n.rb:55:in `with_locale'
lib/gitlab/i18n.rb:61:in `with_user_locale'
app/controllers/application_controller.rb:476:in `set_locale'
lib/gitlab/error_tracking.rb:50:in `with_context'
app/controllers/application_controller.rb:541:in `sentry_context'
app/controllers/application_controller.rb:469:in `block in set_current_context'
lib/gitlab/application_context.rb:52:in `block in use'
lib/gitlab/application_context.rb:52:in `use'
lib/gitlab/application_context.rb:20:in `with_context'
app/controllers/application_controller.rb:462:in `set_current_context'
lib/gitlab/metrics/elasticsearch_rack_middleware.rb:24:in `call'
lib/gitlab/metrics/redis_rack_middleware.rb:22:in `call'
lib/gitlab/middleware/rails_queue_duration.rb:29:in `call'
lib/gitlab/metrics/rack_middleware.rb:17:in `block in call'
lib/gitlab/metrics/transaction.rb:54:in `run'
lib/gitlab/metrics/rack_middleware.rb:17:in `call'
lib/gitlab/request_profiler/middleware.rb:17:in `call'
lib/gitlab/middleware/go.rb:20:in `call'
lib/gitlab/etag_caching/middleware.rb:13:in `call'
lib/gitlab/middleware/multipart.rb:140:in `call'
lib/gitlab/middleware/read_only/controller.rb:51:in `call'
lib/gitlab/middleware/read_only.rb:18:in `call'
lib/gitlab/middleware/same_site_cookies.rb:27:in `call'
lib/gitlab/middleware/basic_health_check.rb:25:in `call'
lib/gitlab/middleware/handle_ip_spoof_attack_error.rb:25:in `call'
lib/gitlab/middleware/request_context.rb:23:in `call'
config/initializers/fix_local_cache_middleware.rb:9:in `call'
lib/gitlab/metrics/requests_rack_middleware.rb:60:in `call'
lib/gitlab/middleware/release_env.rb:12:in `call'

Can someone please give me a hint, how to fix this?

Thanks